This invention relates generally to electric lamps, and particularly to those for use on motor vehicles such as, typically, headlamps. Still more particularly, the invention pertains to improvements in or relating to aiming mechanisms for aiming and retaining the beams of headlamps or the like in proper angular positions with respect to the vehicle.
Aimable headlamps may be divided into two broad categories according to the member to be tilted, both vertically and horizontally, for aiming the beam. In one such design the complete headlamp unit, comprising an electric lighting bulb or bulbs, a reflector or reflectors and a lens, is tilted relative to the vehicle or to the lamp housing fixed to the vehicle. The other design is such that only the reflector is tilted relative to the lamp body or the like which is fixed to the vehicle.
In either case, a typical aiming mechanism comprises a pivotal connection such as a ball-and-socket joint between a tiltable member and a fixed member, and two aiming screws extending between the two members. The relative placement of the pivotal connection and the aiming screws is such that the first of the two aiming screws is displaced horizontally, and the second vertically, from the pivotal connection. The tightening or loosening of the first aiming screw results, therefore, in the tilting of the tiltable member about a vertical axis passing through the pivotal connection and the second aiming screw. Similarly, the manipulation of the second aiming screw results in the tilting of the tiltable member about a horizontal axis passing through the pivotal connection and the first aiming screw.
A problem has been encountered with aiming mechanisms of the foregoing general construction. Conventionally, each aiming screw was rotatably supported by the fixed member and screw-threadedly engaged with a nut affixed to the tiltable member. When each aiming screw was turned in either direction, the nut engaged therewith had to travel arcuately with the tiltable member about either of the two axes but was nevertheless constrained to rectilinear displacement on the aiming screw. The resulting conflict between the circular and the linear motions impeded the smooth tilting of the tiltable member.
This drawback of the prior art became even more pronounced when a leveling actuator was employed in substitution for one of the aiming screws. As the name implies, the leveling actuator is intended for automatic readjustment of the beam angle in a vertical plane in response not only to changes in the load on the vehicle but also to the pitching of the vehicle during travel. The leveling actuator is required to act very quickly in order to readjust the beam angle in compensation for vehicle pitching. The conventional aiming mechanisms with their conflicting motions have presented a serious bar to the advent of automatically leveling headlamps of truly satisfactory performance.